Lithographic plate and method of making same



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Patented Nov. 7, 1939- UNITED, STATES PATENT OFFICE LITHOGRAPHIC PLATE AND METHOD OF MAKING sum William H. Wood, Redford, Ohio, aaaignor to Harris-Seybold-Potter Company,- Ohio, a. corporation of Delaware Cleveland,

No Drawing. Application June 10, 1937,

'SerialNo. 148,563

'14 Claims- (CI. -54

,The present invention relating, as indicated,

to lithographic plates and method of making the tive to the action of light by; the addition of a sensitizing agent such as ammonium chromate or dichromate. After the plate has been coated and allowed to dry, it is exposed to light in the form of an image of the subject which is to be printed. The light hardens the albumin coating to the solvent action of water thus forming a reproduction of the subject in hardened albumin and leaving the remaining portions of the albumin coating relatively unhardened. A suitable developing ink'is applied to the coating and then the unhardened areas are removed by dissolving them away with water. After application of an etching solution to clean the non-image portions of the plate and render them receptive to water, the plate is in condition for printing.

The above process which is in common use is subject to numerous disadvantages and limitations, chief among which are: (1) non-uniformity of different albumin coatings as regards their sensitivity to light; (2) variation in sensitivity of the same coating to light with the elapsed time between coating and exposure; (3) rapid deterioration of the albumin coating solution and of the coating after application to the plate; (4) large I variation of sensitivity to light with variations in humidity and temperature conditions; (5) 'short life on the press because of low mechanical strength and lack of resistance to the etching materials used in the dampening solution; (6) limitation of the sensitivity of the albumin coatings to the violet and ultra-violet portions of the spectrum of light sources used for exposure; and (7) the necessity for intense sources of illumination and relatively long exposure times in order to produce satisfactory results.

It is an object of the present invention to provide a novel coating material and process which will overcome the above disadvantages and limb tations in large measure and which will result in the production of a lithographic plate having superior printing qualities.

' a given water solution, e. g., a 3% solution, varies,

To the accomplishment of the foregoing and related ends, said invention, then, consists of the steps and ingredients hereinafter fully described and particularly pointed out in the claims, the

following description setting forth in detail cer- 5' tain steps and product exemplifying my invention, such disclosed procedure and product con stituting, however, but one of various applications of the principle of the invention.

The present invention is based on the discov- 10 ery that derivatives of polyvinyl alcohol, and particularly halogenated derivatives thereof, may be employed as a material for coating lithographic plates in place of the albumin coating commonly used. Aside from possessing in itself highly use- W ful characteristics'for the indicated purpose, a coating composed of a compound of the type in question lends itself to certain novel treatments in the course of making the finished plate.

Vinyl alcohol or ethanol (CH:CH.OH) occurs 20 in commercialether, but has not yet been isolated (B22, 2863). However, polyvinyl alcohol is now commercially available and I have found that the product obtained by reacting on such polyvinyl alcohol with a halogen, preferably chlorine, (bromine or iodine also yield a satisfactory product) may be readily dissolved or dispersed in water. Such solution, the term as here employed connoting either a true solution or a line colloidal suspension, may then be applied to 30 the surface to be treated and upon evaporation of the solvent or vehicle, a film of the halogenated polyvinyl alcohol is deposited as a uniform coatns The actual formula of polyvinyl alcohol is not 35 definitely known, but may be represented as So far as I am aware, it has not been definitely 0 established whether the halogen is added at the ends of the chain or whether it replaces one or more of the side-attached hydrogen atoms.

Commercial polyvinyl alcohol comes in the form of a white dry powder, but the viscosity in corresponding with what is termed a low, mediumand high viscosity product. Presumably the difference in viscosity is attributable to difrences in the degree of polymerization of the alcohol. My improved halogenated derivative may be made from the polymerized alcohol, irrespective of the degree of polymerization. Both the chlorinated and brominated derivative in dry form is a flue white granular powder readily dis- 55 solving in water at 80 degrees C. to give awhite iridescent solution, dissolving more slowly at lower temperatures.

In employing the foregoing product to make plates for use in lithographic printing, the colloidal material, either alone or forming part of a mixture with other suitable coating material,

I is applied to the surface of a metal plate, e. gl,

zinc' or aluminum, or a plate having a metallic surface. The coating material may be sensitized either'before or after it is thus applied and is then subjected to the action of light, printing thereon an image by means of light, and subsequently the image portions of the plate are rendated ink receptive and the non-image portions water receptive or ink repellent. In the process as above outlined, the steps subsequent to the coating of the plate may be carried out by the use of materials and methods commonly used in the preparation of plates coated with albumin, such as the nsual sensitizing 1 agents, ordinary developing inks and ordinary developing and etching methods, and superior results will be obtained in which some or all of the 5 disadvantages listed as inherent in the use of the present type of albumin coatings are overcome. While the light sensitizing agent may be added or incorporated in the colloidal material that forms the coating prior to the application of the coating to the plate, it is possible by the use of my improved coating material to apply such agent by bathing the coated plate in a solution, for example, an alcohol solution, of the sensitizing agent. The sensitizing of lithographic plates by bathing them after coating is in itself an important advance in the art since it enables coated plates to be stored a considerable time, as well as to be shipped some distance, prior to .their being used.

The solution of polyvinyl alcohol derivative is used preferably in a 2m 5% solution in water. A sensitizer consisting of ammonium dichromate or other chromium salt may be added in the ratio of one part of such salt to three parts of the polyvinyl alcohol derivative, but ratios as high as five parts of the chromium salt to one part of polyvinyl alcohol derivative maybe used, such ratios being by weight. The viscosity of the solution resulting from the halogenation of polyvinyl alcohol or derivative thereof, where chlorine or bromine is the halogen used, will be less than that of the original material reacted on. For use in making lithographic plates, the resulting solution should be of such viscosity as to render it spreadable by whirling or other method commonly used in applying coatings to such plates; in other words, it should not be of such high viscosity as to be unmanageable for such use.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the composition and method herein disclosed, provided the ingredients 0). steps stated by any of the following claimsfor the equivalent of such stated ingredients or steps be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A coating material for lithographic plates,

3. A coatingmaterial for lithographic-plates,

which comprises a water-soluble chlorinated polyvinyl alcohol.

4. A coating material for lithographic'plates, which comprises a water-soluble brominated polyvinyl alcohol.

5. A coating material for lithographic plates, which comprises a water-soluble halogenated polyvinyl alcohol and a light-sensitizer chromium compound.

6. As a new article of manufacture, a plate for use in lithographic printing having a surface the base whereof is a water-soluble reaction product of a halogen and polyvinyl alcohol.

7. As a new article of manufacture, a plate for use in lithographic printing having a surface comprising awater-soluble halogenated polyvinyl alcohol anda light-sensitizing agent.

8. As a new article of manufacture, a plate for use in lithographic printing having a surface comprising a water-soluble chlorinated polyvinyl alcohol.

9. As a new article of manufacture, a plate for use in lithographic printing having a surface comprising a water-soluble brominated polyvinyl alcohol.

10. As a new article of manufacture, a plate,

for use in lithographic printing having a surface comprising a water-soluble halogenated polyvinyl alcohol and a light-sensitizing chromium compound.

11. ln preparing a plate for use in lithographic printing, applying to the plate a water-soluble reaction product of a halogen and polyvinyl alcohol.

12. In preparing a plate for use in lithographic printing, providing on the plate a water-soluble halogenated polyvinyl alcohol sensitized to light.

13. In preparing a plate for use in lithographic printing, applying to the plate a water-soluble reaction product of a halogen and polyvinyl alcohol, and subsequently treating the surface with a light-sensitizing agent.

14. In preparing a plate for use in lithographic printing, applying to the plate a water-soluble reaction product of a halogen and polyvinyl alcohol, and subsequently bathing the surface with a solution of a light-sensitizing chromium compound.

WILLIAM H. WOOD. 

